TNF is believed to be a key cytokine in the inflammatory response that is the hallmark of inflammatory bowel disease (ibd). Open label, Phase I trials of a chimeric anti-tnf monoclonal antibody, cA2, have shown promising results in the treatment of patients with severe, refractory IBD. The purpose of this study is to determine the safety, tolerance, immunogenicity and pharmacokinetics of cA2 in patients with severe ulcerative colitis refractory to intravenous corticosteroid therapy, and to determine its efficacy as a treatment for severe ulcerative colitis.